1. Technical Field
This disclosure relates generally to an image forming apparatus, and more particularly to an image forming apparatus using a recording head including a liquid ejection head that ejects liquid droplets.
2. Description of the Background
One example of related-art image forming apparatuses such as printers, copiers, plotters, facsimile machines, and multifunction devices having two or more of printing, copying, plotting, and facsimile functions is an inkjet recording device employing a liquid ejection recording method. The inkjet recording device includes a recording head that ejects droplets of a recording liquid such as ink onto a sheet of a recording medium while the sheet is conveyed to form an image on the sheet.
Examples of the inkjet recording device include a serial-type image forming apparatus, in which the recording head ejects liquid droplets while moving in a main scanning direction to form an image on the sheet as the sheet is moved in a sub-scanning direction perpendicular to the main scanning direction, and a line-type image forming apparatus equipped with a line-type recording head that ejects liquid droplets and does so without moving to form an image on the sheet as the sheet is moved in the sub-scanning direction.
A maintenance mechanism that maintains and recovers performance of the recording head is essential for the image forming apparatus employing the liquid ejection recording method. One of the functions of the maintenance mechanism is to discharge bubbles, foreign substances, coagulated ink, and so forth present in the recording head through nozzles in the recording head in order to prevent irregular ejection of the ink from the nozzles in the recording head.
In addition, a full-color image forming apparatus that forms full-color images using the liquid ejection recording method generally includes two separate recording heads, that is, a recording head that ejects black ink droplets (hereinafter referred to as the first recording head) and a recording head that ejects color ink droplets (hereinafter referred to as the second recording head). In such a full-color image forming apparatus, not only black ink but also color ink is ejected for maintenance of the recording heads even when monochrome printing is performed using only the first recording head, causing a waste of color ink and a concomitant cost increase.
In order to solve this problem, various techniques have been proposed. In one example, an image forming apparatus includes a scanning-type carrier which is moved reciprocally back and forth by a drive force; a first carriage that ejects black ink droplets and a second carriage that ejects color ink droplets, each detachably attachable to the carrier; a detector that detects that the carriages attached to the carrier pass through a certain reference position in a direction of movement of the carrier; and a control unit that controls movement of the carrier using as a reference a time when the detector detects the carriages.
Another example of an image forming apparatus includes a first carriage that ejects black ink droplets, a second carriage that ejects color ink droplets, and a scanning element serving as a carrier. Each of the first and second carriages and the carrier has a shielding plate. An interval between the shielding plates respectively provided to the first carriage and the carrier when the first carriage and the carrier are coupled together is different from an interval between the shielding plates respectively provided to the second carriage and the carrier when the second carriage and the carrier are coupled together in a direction of movement of the carrier. Accordingly, which carriage is coupled to the carrier is determined based on a timing detected by an optical sensor that detects movement of the shielding plates.
In yet another approach, an image forming apparatus includes a first carrier to which a first image forming head is replaceably installed, a second carrier to which a second image forming head is replaceably installed, and a connector separatably connectable to each of the first and second carriers. The image forming apparatus further includes a scanner that moves one or both of the first and second carriers connected to the connector in a main scanning direction. The first and second image forming heads eject liquid droplets of the same colors.
However, in the above-described configurations in which the carriages are connected to each other with the carrier or the scanner serving as an intermediate member, the accuracy with which the relative positions of the carriages are secured is decreased due to the use of the intermediate body, thus degrading image quality.